Process for preparation of metallocenes



United States Patent Office 3,382,268 Patented May 7, 1968 3,382,268PROCESS FOR PREPARATION OF METALLOCENES Michael Cais, 21 Smolenskin St.,Ahusa, Haifa, Israel No Drawing. Continuation of application Ser. No.314,855, Oct. 9, 1963. This application Apr. 11, 1967, Ser. No. 630,139

6 Claims. (Cl. 260-439) This application is a continuation ofapplication No. 314,855, filed Oct. 9, 1963, and now abandoned.

This invention relates to the preparation of the metallocenes.

Metallocenes are dicyclopent-adienyl metal compounds. Best known amongthem is ferrocene, i.e. the metallocene in which the metal component isiron. Other known metallocenes comprise those in which the metalcomponent is a transition metal, e.g. nickel, cobalt, ruthenium, or thelike. Ferrocene can be used for a large number of different technicalpurposes, for most of which the other known metallocenes may also besuitable. For the sake of brevity, the invention will be explained andexemplified hereinafter with reference to ferrocene, but the widerapplicability of the invention remains understood.

On a laboratory scale, ferrocene has so far been prepared by a methodwhich takes a long time to produce ferrocene in batches which do notexceed 20-25 g. In this method a solution of cyclopentadiene in aprimary or secondary aliphatic amine, usually diethylamine, is added toa slurry of ferrous chloride in a suitable anhydrous solvent, e.g.diethyl ether, the mixture is stirred for 14-16 hours, then theferrocene formed is extracted with petroleum ether, from the extract thesolvent is evaporated and the residue is purified, e.g. byrecrystallisation 01' sublimation. The preparation of the ferrouschloride slurry takes as a rule about 4 hours, which time has to beadded to the stirring time of 14-16 hours, so that the total time neededfor the preparation of up to 25 g. of ferrocene is 18-20 hours.

It has also been suggested to replace the ferrous chloride with ferrousbromide the preparation of which proceeds much more rapidly than that offerrous chloride, whereby the total time needed for the preparation offerrocene could be lowered by about 3 to 3 /2 hours.

The invention provides a process for the preparation of metallocene inwhich the reaction of the metal compound with cyclopentadiene isconsiderably speeded up and is amenable to the production of largebatches.

In the process according to the invention the reaction mixturecontaining the suspension of a compound of the metal to be combined withcyclopentadiene in a suitable solvent is admixed with a solution ofcyclopentadiene in an amine to which there has been added a catalyticamount of a quaternary alkyl or aralkyl ammonium base.

The quaternary base catalysts encompassed by the present invention canbe generically represented by the following formula:

R 9 [RI IR] on wherein each R individually represents alkyl, aryl orar-alkyl. The alkyl group is preferably 1-5 carbon atoms though longerchain lengths, i.e. 1-10 carbon atoms, are also encompassed by thepresent invention. Benzyl is the preferred aryl group.

Benzyl-trimethyl-ammonium hydroxide has been found to be particularlysuitable. Other suitable quaternary bases are, for example, tetramethyland tetraethyl ammonium hydroxide.

The preferred quantity of catalyst is: 0.05-15% by weight on the basisof the cyclopentadiene added. 1% to 10% is most preferred.

It is believed that the presence of the quaternary ammonium base in thereaction mixture facilitates the ionization (formation of carbanions) ofthe cyclopentadiene, and the appreciably increased concentration ofcyclopentadienyl anions makes for a speedier reaction with the metalions to form the desired metallocene.

The amine used as a cyclopentadiene solvent may be a primary, secondaryor tertiary alkyl or aralkyl amine, but for the purposes of thisinvention the term amine also includes heterocyclic nitrogen bases suchas pyridine, pyrrole, quinoline, pyrimidine and the like.

Saturated heterocyclic nitrogen bases contemplated by the presentinvention are those having the formula:

C E) l wherein R is H, aralkyl or alkyl of 1-10 carbon atoms and n is4-7. The invention is not restricted to saturated heterocyclic nitrogenbases, however, but also encompasses unsaturated heterocyclic nitgrogenbases such as the pyrimidines.

Where the method according to the invention is applied to thepreparation of ferrocene, ferrous bromide is used with particularadvantage as the ferrous halide serving as a starting material. However,any other form of the ferrous ion may be employed. Thus other halidessuch as ferrous chloride are encompassed by the present invention. Achelate may be employed if desired.

The metals particularly contemplated by the present invention are thetransition metals, i.e., those having atomic numbers of 22-28 and 40-46such as manganese, cobalt, nickel, vanadium, etc.

It has been found that the synthesis of g. batches of ferrocene can beachieved in a total time of about six hours, as compared to the nearlytwenty hours needed in the conventional method (with ferrous chloride)for the preparation of about 25 g. of ferrocene.

The invention is illustrated by the following example to which it is notlimited.

Example 128 g. (0.8 mole) of bromine was added under nitrogen is smallportions over a period of 20 minutes to a suspension of 89.6 g. (1.6mole) of iron powder in 1 liter of dimethoxyethane. The temperature ofthe reaction mixture was kept at 20 C. by cooling with iced water. Afterall the bromine had been added to the mixture the latter was refluxedunder nitrogen for 20 minutes, then cooled to about 10 C. and to itthere was introduced over a period of 10 minutes under vigorous stirringand with continued cooling a mixture of 105.6 1.6 mole) ofcyclopentadiene, 500 ml. of diethylamine and 5 ml. of a 40% by weightmeth-anolic solution of benzyl-trimethylammonium hydroxide. The mixturewas then stirred under nitrogen for another 2 hours at room temperature.Then the solvents were evaporated in vacuo (at the reduced pressureproduced by a water jet pump) and the residue was extracted with sevensuccessive portions of petroleum ether (B.P. 60-80 C.) of 700 ml. each.From the combined petroleum ether extracts the petroleum ether wasevaporated and a residue of about 98 g. of ferrocene of MP. 172-174 C.was obtained which did not require further purification.

What is is claimed is:

1. In a process for the preparation of metallocenes wherein the reactionmixture contains a suspension of a 3 diene in an amine. the improvementwhich comprises catalyzing said reaction with a material taken from theclass consisting of 1 RI\IR wherein R is a radical taken from the classconsisting of aikyl, aryl and aralkyl wherein the alkyl group has from ito 1 carbon atoms.

2. A process according to claim 1, wherein the catalyst isbenzyl-trimethyl-ammonium hydroxide.

.3. A process according to claim 1, wherein ferrous bromide is used asthe metal compound.

4. A process according to claim 1, wherein the amount of said catalystis us to about 15% based on the cyclopentadiene.

5. A process according to claim 1, wherein the catalyst is tetramethylammonium hydroxide.

6. A process according to claim 1, wherein the catalyst is tetraethylammonium hydroxide.

No references cited.

TOBIAS E. LEVOW, Primary Examiner.

A. P. DEMERS, Assistant Examiner.

1. IN A PROCESS FOR THE PREPARATION OF METALLOCENES WHEREIN THE REACTIONMIXTURE CONTAINS A SUSPENSION OF A COMPOUND OF THE METAL TO BE COMBINEDWITH CYCLOPENTADIENE IN AN AMINE, THE IMPROVEMENT WHICH COMPRISESCATALYZING SAID REACTION WITH A MATERIAL TAKEN FROM THE CLASS CONSISTINGOF